• Sat, 01/29/2011 - 02:14
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A huge vortex of hot air was coming straight toward them, according to the LIDAR, but the video cameras saw nothing. As the research team huddled in their van, an invisible pillar of rotating air, thousands of feet high, churned relentlessly closer. The vortex seemed to stalk them as they marked its distance; first two kilometers, then one, then 500 meters.

The van shook as it was engulfed in a swirl of wind, and someone shouted "It's right on top of us!" The team burst from their vehicle, unable to contain their excitement. Shouts punctuated the dry Arizona air as they watched desert brush bend to the wind. The phantom left as quickly as it came, with Doppler wind speed measurements from the Light Detection and Ranging (LIDAR) instrument the only evidence of its passing.

(LIDAR is similar in principle to RADAR. LIDAR uses pulses of laser light to measure the distance to objects, while RADAR uses pulses of radio waves to make the measurement.)

The team believes they made the first Doppler LIDAR measurements of an invisible dust devil. "Some researchers think a dust devil may need dust to sustain itself, but here we recorded a very large one that was essentially free of dust for a substantial part of its lifetime," said Dr. Brent Bos of NASA's Goddard Space Flight Center in Greenbelt, Md.